Returns the non-archived letters of the authenticated client with minimal fields per item.
Use the GET /letters/{letterId} endpoint to retrieve the full details of a letter.

Pagination

Results are paginated with the limit and page query parameters. Both values are clamped,
never rejected: limit is capped at 200 (default 50), an invalid page falls back to 1.
The meta object of the response tells whether more results are available (hasMore)
and how many items exist in total (total).